The main target cells for Epstein-Barr virus (EBV) infection and persistence are B lymphocytes, although T and NK cells could also be infected. The team of S. Latour in collaboration with the team of Paul Farrell (Imperial College London) characterized the EBV present in 21 pediatric and adult patients, treated in France for a serie of diseases leading to infection of T or NK cells called “Chronic active EBV” or CAEBV. In 30% of cases, the EBV genome has large deletions that are different from one patient to another located in the vicinity of the BART region. These deletions appear and are selected independently from patient to patient. These results support the role of these deletions in these atypical forms of EBV infection.